The radio data system (RDS) is intended for application to VHF/FM audio broadcasts in the range 87.5 MHz to 108 MHz; these may carry either stereophonic or monophonic programs. The main objectives of RDS are to enable improved functionality of FM receivers and to make them more user friendly. This is achieved through the use of features such as program service (PS) name, program type (PTY) and, where applicable, automatic tuning for radios incorporated into mobile devices.
RDS is defined by the European Broadcasting Union (EBU)/Cenelec Standard EN50067: 1998, “Specification of the Radio Data System”. This standard is compatible with the United States radio broadcast data system defined by their National Radio Systems Committee in the specification of the Radio Broadcast Data System, dated 9 Apr. 1998. In the following, it should be understood that the term RDS refers to both the Radio Data System and the Radio Data Broadcasting System (RDBS).
FIG. 1 shows the structure of the baseband coding of the RDS standards.
The largest element in the structure is called a group, consisting of 104 bits. Each group contains four blocks of 26 bits each. Each block contains an information word and a check word. Each information word comprises 16 bits, and each check word comprises 10 bits.
Each group contains message information; the message format and addressing structure are shown in FIG. 2. The first block in every group always contains a program identification (PI) code. The first four bits of the second block of every group are allocated to a 4-bit code that specifies how the information within the group is to be applied. Groups will be referred to as type 0 to 15 according to binary weighting A3=8, A2=4, AI=2, Ao=1. For each type (0 to 15) two versions can be defined. The version is specified by a fifth bit (Bo) of block 2. a) Bo=0: the PI code is inserted in block 1 only. This defines version A of the RDS encoding systems. b) Bo=1: the PI code is inserted in block 1 and block 3 of all group types.
This defines version B of the RDS encoding systems.
Each block contains a Group Type Code (GTC) defining the nature of the information word of the block.
A mixture of version A and version B groups may be transmitted on one particular FM radio station. A program type code (PTY) and the traffic program identification (TP) occupy six locations in block 2 of every group.
The PI, PTY and TP codes can be decoded without reference to any block outside the ones that contain information relating to one of these codes. This is important to minimise acquisition time for these kinds of message and to retain the advantages of the short (26-bit) block length. To permit this to be done for the PI codes in block 3 of version B groups, a special offset word (commonly defined as C′) is used in block 3 of version B groups. The occurrence of offset C′ in block 3 of any group can then be used to indicate directly that block 3 is a PI code, without any reference to the value of Bo in block 2.
Repetition rates of some of the main features of RDS are defined in the standard. A total of four type OA groups are required to transmit an entire program service (PS) name, and therefore four type OA groups are required per second according to the standard. The repetition rate of the type OA group may be reduced if more capacity is needed for other applications. A minimum of two type OA groups per second is necessary to ensure correct functioning of PS and alternative frequency (AF) features.
Circuits for receiving and decoding both audio and data components of an FM radio broadcast are known in the art. Indeed, an example of an FM receiver demodulator having an RDS demodulator and decoder is given in the radio broadcast data system standard.
Mobile devices, for example mobile phones, smartphones and car stereos, incorporating FM radio receivers require occasional or sometimes frequent retuning due to spatial variation of intensity of FM radio signals. Further, the availability of radio stations varies between geographical regions. Normally, a user of a mobile radio will search a frequency band for a desired radio station, using a scan or seek function of the mobile radio. The mobile radio will scan for a signal and once locked on to a station, will receive and decode a PS code of the station in order to establish a respective program station name. The mobile radio may then display the program station name.
Due to user interface constraints of a typical mobile radio user interface, this is the most commonly used technique for searching an FM radio band. Further, due to the presence of alternative frequencies for a particular station, it is possible that the particular station may be encountered more than once during a search as described above.
An FM radio receiver with RDS may only perform a search on the whole frequency spectrum of the FM radio band. This is undesirable as a user travelling from their home region to another region may wish to listen to a particular radio station they heard while last visiting the another region, the particular radio station having a particular frequency. The user may not be able to remember the particular frequency of the particular radio station, but may be able to remember the entirety of or a portion of the radio station name.
With known FM radio receivers, the user will be forced to scan the whole frequency spectrum of the FM radio band manually in order to find the particular radio station that they wish to listen to.
It is known for a mobile phone to be caused to download a channel list and to use the channel list to determine a frequency at which a desired programme is broadcast. However, it cannot be relied upon here that the radio station at a frequency has sufficient signal quality to provide a suitable user experience.
WO 2005/062507 discloses an RDS or RDBS receiver that scans through the FM radio band and detects radio stations that are broadcasting in the band. The receiver decodes RDS information including PS information for each of the detected stations and presents this information on a display 10, e.g. as a list of radio stations. To select a station, the user may input a search criterion, such as complete or partial PS name of a desired radio station. The receiver may perform a scan of the whole available spectrum, at each detected radio station receiving RDS data until the PS name has been decoded, and store the PS name along with information identifying the frequency at which the PS name was found. In this way, a user can quickly access a radio station having a programme name that includes text entered into a search request by the user.
It is an aim of embodiments of the present invention to solve or at least mitigate one or more of the problems described above.